In a video format, images are typically captured in a series of video fields. These video fields are made up of hundreds of horizontal scan lines, which are essentially "slices" of the image in the video field. Each scan line is made up of a plurality of pixels. The raw video data which forms the pixels is YUV data. Each pixel has varying YUV values which can be converted into varying red, blue and green (RGB) values which determine the color of each pixel. The RGB values are numeric values which indicate a level of each color which makes up the color of each pixel. In order to conserve bandwidth in the playback of the video images, consecutive fields may be interlaced to make one composite video frame from two consecutive video fields. Interlacing is done by vertically alternating horizontal scan lines from each consecutive field to form one video frame. In the NTSC video format, video images are captured at 60 fields per second. Interlacing two consecutive fields results in video which is transmitted at 30 frames per second. There are other video formats which have different scan rates, such as PAL, which has a scan rate of 50 fields per second or 25 frames per second.
Video field interlacing is schematically shown in FIG. 1A and FIG. 1B. FIG. 1A shows two consecutive video fields A.sub.1, A.sub.2. Each of the video fields A.sub.1 and A.sub.2 are made up of hundreds of horizontal scan lines which make up an image which is depicted in the field. In FIG. 1A, the scan lines which make up field A.sub.1 are labeled A.sub.L1, and the scan lines which make up field A.sub.2 are labeled A.sub.L2. As stated above, video fields for NTSC video are typically shot at approximately 60 fields per second. FIG. 1B schematically shows how fields A.sub.1 and A.sub.2 are interlaced to form video frame A.sub.12. As shown in the figure, video frame A.sub.12 comprises the scan lines A.sub.L1 and A.sub.L2 in an alternating fashion from the top of the frame to the bottom of the frame. This interlacing of video fields A.sub.1 and A.sub.2 results in a video transmission rate of approximately 30 frames per second.
Conventionally, once the video fields are interlaced, editing is performed either by displaying both fields, or by displaying just one field and doubling the scan lines to fill the frame.
Displaying both fields presents a problem because there is a slight timing offset between each field. Therefore, when the fields are interlaced to form the video frame, the image may be somewhat choppy or blurred due to the difference in time between the images in each field. During the editing process, objects which are moving in an image of the video field cannot be accurately outlined, because moving objects will be displayed in two separate locations in the frame, one location for each video field.
Doubling the scan lines of a field is done by a process called "scan doubling." In the process of scan doubling, each scan line in the video field is doubled, in order to fill the entire frame. The doubled field is then edited. However, since there is a difference in time between each video field, scan doubling tends to display data in the video frame which may be false or misleading, since it is compensating for the time offset between each video field. Scan doubling causes half of the spatial information of the frame to be lost because it is contained in the video field which is not shown in the scan doubled frame. This is particularly problematic when the fields contain still or slow moving objects, since the information which is lost is accurate information. This loss of data tends to make editing of the fields difficult, inaccurate and time consuming.